84 BULLETIN OK THE BUREAU OF FISHERIES. 



increased immensely their production, while a constant decrease was observed where the 

 natural reefs were depended upon without sufficient encouragement to cultivation 

 (Massachusetts Commissioners of Fish and Game, 1907). 



This may be an extreme view, but it has been often true. It may be said, on the 

 other hand, that although game protection (of fish, birds, and mammals) has been so 

 frequently only a name in America, there are cases known to all where wild species 

 have thrived under efficient protection combined with restocking in cases of depletion. 

 Past efforts in the conservation of mussels have been largely confined to this limited 

 type of protection. The work has consisted in "artificial propagation" (definition of 

 which follows) and a certain amount of protection by law instituting open and closed 

 seasons to fishing. The closing of certain streams for a number of years, thus creating 

 preserves, has been advocated. Further assistance to nature in recovering from the 

 effects of depletion is suggested in a system of culture, including protection and planting 

 like that employed in restocking with fish. 



The experiments here described furnished practically the first positive data contrib- 

 uting to the development of a system for the culture of fresh-water mussels. It seems 

 worth while to consider whether cultural methods, which the present investigations 

 indicate to be quite feasible, might add anything to the methods now in use. In using 

 the term culture we distinguish from propagation. 



ARTIFICIAL PROPAGATION. 



Artificial propagation as it has been applied to mussels is a method which, as indi- 

 cated above, has been employed by the Bureau of Fisheries some eight years past. 

 The larval mussels are brought in contact with and allowed to infect the host fish, which 

 are then released to spread the mussels under the usual conditions prevailing in nature. 



In the effort to secure increased production of mussels this artificial infection has 

 the following advantage : Whereas in nature the number of mussels which succeed in 

 finding lodgment upon a fish is, as a rule, comparatively small, by artificially bringing 

 parasite and host together the fish is made to carry a much greater number than would 

 otherwise succeed in finding a host. Thus, the number of mussels reaching the juvenile 

 stage is increased. 



The place of shedding of the young mussels from the fish is to a large extent doubt- 

 less a matter of chance. As among marine clams probably those only survive which 

 fall on, or subsequently reach, a favorable bottom. These considerations are largely 

 responsible for the present investigations in the effort to supplement artificial propa- 



ga 10n ' THE CULTURAL METHOD. 



The cultural method as suggested by the present experiments would consist in 

 carrying protection through the second critical period in the life of the young mussel 

 and in planting in favorable localities the mussels obtained. 



PROTECTION. 



In almost all successful attempts at rearing animals or plants protection in critical 

 stages is the important factor. An example from fish culture is the raising of trout. 

 In agriculture the plant or animal is placed under the best environment attainable and 

 protected from destructive forces of all kinds at all stages until used. If finally con- 



